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[net-next-2.6.git] / Documentation / dvb / avermedia.txt

HOWTO: Get An Avermedia DVB-T working under Linux
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   Table of Contents
   Assumptions and Introduction
   The Avermedia DVB-T
   Getting the card going
   Receiving DVB-T in Australia
   Known Limitations
   Further Update

Assumptions and Introduction

   It  is assumed that the reader understands the basic structure
   of  the Linux Kernel DVB drivers and the general principles of
   Digital TV.

   One  significant difference between Digital TV and Analogue TV
   that  the  unwary  (like  myself)  should  consider  is  that,
   although  the  component  structure  of budget DVB-T cards are
   substantially  similar  to Analogue TV cards, they function in
   substantially different ways.

   The  purpose  of  an  Analogue TV is to receive and display an
   Analogue  Television  signal. An Analogue TV signal (otherwise
   known  as  composite  video)  is  an  analogue  encoding  of a
   sequence  of  image frames (25 per second) rasterised using an
   interlacing   technique.   Interlacing  takes  two  fields  to
   represent  one  frame.  Computers today are at their best when
   dealing  with  digital  signals,  not  analogue  signals and a
   composite  video signal is about as far removed from a digital
   data stream as you can get. Therefore, an Analogue TV card for
   a PC has the following purpose:

     * Tune the receiver to receive a broadcast signal
     * demodulate the broadcast signal
     * demultiplex  the  analogue video signal and analogue audio
       signal  (note some countries employ a digital audio signal
       embedded  within the modulated composite analogue signal -
       NICAM.)
     * digitize  the analogue video signal and make the resulting
       datastream available to the data bus.

   The  digital  datastream from an Analogue TV card is generated
   by  circuitry on the card and is often presented uncompressed.
   For  a PAL TV signal encoded at a resolution of 768x576 24-bit
   color pixels over 25 frames per second - a fair amount of data
   is  generated and must be processed by the PC before it can be
   displayed  on the video monitor screen. Some Analogue TV cards
   for  PCs  have  onboard  MPEG2  encoders  which permit the raw
   digital  data  stream  to be presented to the PC in an encoded
   and  compressed  form  -  similar  to the form that is used in
   Digital TV.

   The  purpose of a simple budget digital TV card (DVB-T,C or S)
   is to simply:

     * Tune the received to receive a broadcast signal.
     * Extract  the encoded digital datastream from the broadcast
       signal.
     * Make  the  encoded digital datastream (MPEG2) available to
       the data bus.

   The  significant  difference between the two is that the tuner
   on  the analogue TV card spits out an Analogue signal, whereas
   the  tuner  on  the  digital  TV  card  spits out a compressed
   encoded   digital   datastream.   As  the  signal  is  already
   digitised,  it  is  trivial  to pass this datastream to the PC
   databus  with  minimal  additional processing and then extract
   the  digital  video  and audio datastreams passing them to the
   appropriate software or hardware for decoding and viewing.
     _________________________________________________________

The Avermedia DVB-T

   The Avermedia DVB-T is a budget PCI DVB card. It has 3 inputs:

     * RF Tuner Input
     * Composite Video Input (RCA Jack)
     * SVIDEO Input (Mini-DIN)

   The  RF  Tuner  Input  is the input to the tuner module of the
   card.  The  Tuner  is  otherwise known as the "Frontend" . The
   Frontend of the Avermedia DVB-T is a Microtune 7202D. A timely
   post  to  the  linux-dvb  mailing  list  ascertained  that the
   Microtune  7202D  is  supported  by the sp887x driver which is
   found in the dvb-hw CVS module.

   The  DVB-T card is based around the BT878 chip which is a very
   common multimedia bridge and often found on Analogue TV cards.
   There is no on-board MPEG2 decoder, which means that all MPEG2
   decoding  must  be done in software, or if you have one, on an
   MPEG2 hardware decoding card or chipset.
     _________________________________________________________

Getting the card going

   In order to fire up the card, it is necessary to load a number
   of modules from the DVB driver set. Prior to this it will have
   been  necessary to download these drivers from the linuxtv CVS
   server and compile them successfully.

   Depending on the card's feature set, the Device Driver API for
   DVB under Linux will expose some of the following device files
   in the /dev tree:

     * /dev/dvb/adapter0/audio0
     * /dev/dvb/adapter0/ca0
     * /dev/dvb/adapter0/demux0
     * /dev/dvb/adapter0/dvr0
     * /dev/dvb/adapter0/frontend0
     * /dev/dvb/adapter0/net0
     * /dev/dvb/adapter0/osd0
     * /dev/dvb/adapter0/video0

   The  primary  device  nodes that we are interested in (at this
   stage) for the Avermedia DVB-T are:

     * /dev/dvb/adapter0/dvr0
     * /dev/dvb/adapter0/frontend0

   The dvr0 device node is used to read the MPEG2 Data Stream and
   the frontend0 node is used to tune the frontend tuner module.

   At  this  stage,  it  has  not  been  able  to  ascertain  the
   functionality  of the remaining device nodes in respect of the
   Avermedia  DVBT.  However,  full  functionality  in respect of
   tuning,  receiving  and  supplying  the  MPEG2  data stream is
   possible  with the currently available versions of the driver.
   It  may be possible that additional functionality is available
   from  the  card  (i.e.  viewing the additional analogue inputs
   that  the card presents), but this has not been tested yet. If
   I get around to this, I'll update the document with whatever I
   find.

   To  power  up  the  card,  load  the  following modules in the
   following order:

     * modprobe bttv (normally loaded automatically)
     * modprobe dvb-bt8xx (or place dvb-bt8xx in /etc/modules)

   Insertion  of  these  modules  into  the  running  kernel will
   activate the appropriate DVB device nodes. It is then possible
   to start accessing the card with utilities such as scan, tzap,
   dvbstream etc.

   The frontend module sp887x.o, requires an external   firmware.
   Please use  the  command "get_dvb_firmware sp887x" to download